1. Field of the Invention
The invention relates to an x-ray examination apparatus comprising an x-ray source for emitting x-rays, an x-ray detector for deriving an image signal from an x-ray image, and including a semiconductor element.
2. Description of Related Art
Such an x-ray examination apparatus is known from the European patent application EP 0 642 264.
In the known x-ray examination apparatus the x-ray detector is an x-ray sensor matrix. The known x-ray examination apparatus is provided with a correction unit. The correction unit counteracts disturbances in the image signal which are caused by delayed emission of electric charges from the x-ray image sensor matrix. Incident x-rays release electric charge carriers, i.e. photocharges, notably photoelectrons, in the x-ray image sensor matrix and these electric charges are detected. The signal levels of the image signal represent the detected electric charges. A part of the electric charge carriers can be trapped in a trap-state, be retained in such a trap-state, and can escape from the trap-state at a later stage and are detected as electric charges with a delay. If the image signal with the disturbances were applied to a monitor for displaying the image information, not only the image information of the instantaneous image would be reproduced, but at the same time also image information of a previously picked-up image. As a result after-images would be displayed together with the instantaneous image.
The correction unit of the known x-ray examination apparatus utilizes an intricate mathematical model based on physical considerations for the trapping and subsequent release of electric charge carriers so as to correct disturbances due to electric charge carriers emitted in a delayed fashion. A drawback of the correction unit of the known x-ray examination apparatus is that the computations necessary to obtain the corrected image signal are rather complicated so that a powerful arithmetic unit is required. A rather fast and therefore quite expensive arithmetic unit is required to keep short the time which is needed for the correction of the image signal so as to render the known x-ray examination apparatus suitable for imaging rapid dynamic processes. Moreover, the required programming of the arithmetic unit is complicated, so that well educated staff is needed to set up the correction unit.